The Burlington Limestone is named for the city of Burlington, Des Moines County, Iowa, where the formation is well exposed and about 70 feet thick. In Illinois, the Burlington extends from Henderson County in the northwest across a roughly triangular area southward to Jackson County and eastward to Iroquois County. Good outcrops are found in the Mississippi River bluffs from Quincy, Adams County, to near Alton, Madison County. In the vicinity of Quincy the lower 25 feet is relatively pure and is quarried as the "Quincy Lime." In the southern area the Burlington and the overlying Keokuk can be distinguished only by their fossils and are generally referred to as the Burlington-Keokuk Limestone.